Influence of Ni/Zn double coating on the steel on penetration welding-brazing by CMT arc-laser hybrid heat source

Abstract To improve interfacial inhomogeneous temperature distribution and weld appearance of butt welding-brazing of steel/aluminum dissimilar metals, a hybrid heat source method combining laser penetration welding with CMT arc was developed. The Ni/Zn double coating was prepared on the surface of steel to improve the interfacial reaction and achieve fluxless process. The welding characteristics of bare steel/aluminum alloy, Ni coated steel/aluminum alloy, and Ni/Zn double coated steel/aluminum alloy were comparatively studied. Transmission electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS) were used to analyze the interfacial microstructures of the joint. The results showed that the fluxless process were implemented by preparing Ni/Zn double coating on the surface of steel. The interfacial reaction between liquid Al and solid steel was obstructed to some extent by Ni/Zn double coating. The thickness of intermetallic compounds (IMCs) was reduced significantly. The interfacial reaction layer consisted of Fe2Al5 near the steel side and Fe4Al13 near the aluminum side. No continuous Ni-Al IMCs were found at the Fe/Al butt interface. The maximum tensile strength of Ni coated steel/aluminum joint was up to 93.4 MPa, which increased by 12% than that of the bare steel/aluminum joint. The maximum tensile strength of Ni/Zn double coated steel/aluminum joint was up to 112.6 MPa, which increased by 35% than that of the bare steel/aluminum joint. On this basis, the fluxless wetting and interfacial reaction mechanisms were revealed.